1. Field of the Invention
The present invention relates to a so-called head-mounted type of display apparatus (head-mounted display) which permits a user to view a display image with the display apparatus being mounted on a predetermined portion of the user, such as the head or the face.
2. Description of Related Art
Conventionally, this kind of display apparatus has not had the function of informing a user himself/herself how long the user has been using the display apparatus.
In recent years, this kind of display apparatus has been used in more and more applications which enable users to view images or the like. Computer games are the most popular of such applications. Unlike normal television screens, this kind of display apparatus can easily create a closed space, so that a user can be more deeply immersed in the world of a game. Furthermore, such a display apparatus is provided with a head detecting device for detecting the motion of the head of the user, and can realize virtual reality (VR) by varying a display image according to the detection value of the head detecting device. This kind of display apparatus can also be used as a computer display. The use of the display apparatus enables a user to operate a computer anywhere without the need to use a large CRT display and without worrying whether someone is peeping at the user's display.
This kind of display apparatus using a small liquid crystal display panel is arranged as shown in FIG. 1. In the arrangement shown in FIG. 1, light emitted from a backlight 1902 passes through a display 1901 such as a liquid crystal display panel, and is made incident on an entrance surface 1900a of an optical element 1900. The light passing through the entrance surface 1900a is made incident on a reflecting surface 1900b of the optical element 1900 at an angle of incidence not less than a critical angle and is totally reflected from the reflecting surface 1900b toward a total reflection surface 1900c of the optical element 1900. The light is again totally reflected by the total reflection surface 1900c and is made incident on the reflecting surface 1900b at an angle of incidence not greater than the critical angle. The light incident at the angle of incidence not greater than the critical angle is conducted to a pupil 1908 of a user and an image is displayed by the display 1901, so that the user can view the displayed image.
However, the above-described conventional apparatus has the problem that a user may continuously use the display apparatus over a long time without noticing the lapse of use time.
In addition, the conventional display which is used as display means for a game or a computer has the problem that a user often tends to immerse himself/herself in a display picture and continuously wear the display apparatus over a long time, as well as the problem that it is troublesome for the user to frequently put on and take off the display apparatus.
Furthermore, regarding the display apparatus shown in FIG. 1, the user may continuously use the display apparatus over a long time without noticing the lapse of use time. Although there is a method of displaying clock information in the display 1901 to prevent this problem, this method may not agree with the intention of the user, because the display apparatus is intended to create virtual reality.